Business Process Execution Language. for Web Services. Version May Authors (alphabetically):

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1 Business Process Execution Language 5 May 2003 Authors (alphabetically): Tony Andrews, Microsoft Francisco Curbera, IBM Hitesh Dholakia, Siebel Systems Yaron Goland, BEA Johannes Klein, Microsoft Frank Leymann, IBM Kevin Liu, SAP Dieter Roller, IBM Doug Smith, Siebel Systems Satish Thatte, Microsoft (Editor) Ivana Trickovic, SAP Sanjiva Weerawarana, IBM for Web Services Version 1.1 Copyright 2002, 2003 BEA Systems, International Business Machines Corporation, Microsoft Corporation, SAP AG, Siebel Systems. All rights reserved. Permission to copy and display the "Business Process Execution Language for Web Services Specification, version 1.1 dated May 5, 2003" (hereafter "the BPEL4WS Specification"), in any medium without fee or royalty is hereby granted, provided that you include the following on ALL copies of the BPEL4WS Specification, or portions thereof, that you make: 1. A link to the BPEL4WS Specification at these locations: Style Definition: Heading 1: Outline numbered + Level: 1 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0" + Tab after: 0" + Indent at: 0.4" Style Definition: Heading 2: Outline numbered + Level: 2 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0" + Tab after: 0" + Indent at: 0.4" Style Definition: Heading 3: Outline numbered + Level: 3 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0" + Tab after: 0" + Indent at: 0.4" Style Definition: Heading 4: Outline numbered + Level: 4 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0" + Tab after: 0" + Indent at: 0.4" Style Definition: Heading 5: Outline numbered + Level: 5 + Numbering Style: 1, 2, 3, + Start at: 1 + Alignment: Left + Aligned at: 0" + Tab after: 0.7" + Indent at: 0.7" Style Definition Style Definition Style Definition Style Definition Style Definition Deleted: 31 March Formatted: German Germany Formatted: German Germany Formatted: German Germany Formatted: German Germany Formatted: German Germany Formatted: German Germany Formatted: German Germany Formatted: German Germany Formatted: German Germany Formatted: German Germany Formatted... [1]... [2]... [3]... [4]... [5]... [6] Deleted: The presentation,... [7] 1

2 2. The copyright notice as shown in the BPEL4WS Specification: BEA, IBM, Microsoft, SAP AG and Siebel Systems (collectively, the Authors ) agree to grant you a royalty-free license, under reasonable, non-discriminatory terms and conditions, to patents that they deem necessary to implement the Business Process Execution Language for Web Services Specification. THE Business Process Execution Language for Web Services SPECIFICATION IS PROVIDED "AS IS," AND THE AUTHORS MAKE NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, NON-INFRINGEMENT, OR TITLE; THAT THE CONTENTS OF THE BPEL4WS SPECIFICATION ARE SUITABLE FOR ANY PURPOSE; NOR THAT THE IMPLEMENTATION OF SUCH CONTENTS WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS. THE AUTHORS WILL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF OR RELATING TO ANY USE OR DISTRIBUTION OF THE BPEL4WS SPECIFICATION. The name and trademarks of the Authors may NOT be used in any manner, including advertising or publicity pertaining to the BPEL4WS Specification or its contents without specific, written prior permission. Title to copyright in the BPEL4WS Specification will at all times remain with the Authors. No other rights are granted by implication, estoppel or otherwise. Abstract This document defines a notation for specifying business process behavior based on Web Services. This notation is called Business Process Execution Language for Web Services (abbreviated to BPEL4WS in the rest of this document). Processes in BPEL4WS export and import functionality by using Web Service interfaces exclusively. Business processes can be described in two ways. Executable business processes model actual behavior of a participant in a business interaction. Business protocols, in contrast, use process descriptions that specify the mutually visible message exchange behavior of each of the parties involved in the protocol, without revealing their internal behavior. The process descriptions for business protocols are called abstract processes. BPEL4WS is meant to be used to model the behavior of both executable and abstract processes. BPEL4WS provides a language for the formal specification of business processes and business interaction protocols. By doing so, it extends the Web Services interaction model and enables it to support business transactions. BPEL4WS defines an interoperable integration model that should facilitate the expansion of automated process integration in both the intra-corporate and the business-to-business spaces. 2

3 Status This is a second public draft release of the BPEL4WS specification. BPEL4WS represents a convergence of the ideas in the XLANG and WSFL specifications. Both XLANG and WSFL are superseded by the BPEL4WS specification. Deleted: BPEL4WS and related specifications are provided as-is and for review and evaluation only. The authors hope to solicit your contributions and suggestions in the near future. The authors make no warrantees or representations regarding the specifications in any manner whatsoever. 3

4 Deleted: 8 Contents 1 INTRODUCTION NOTATIONAL CONVENTIONS RELATIONSHIP WITH WSDL WHAT CHANGED FROM BPEL4WS Core Concepts Clarification Terminology Changes Feature Changes CORE CONCEPTS AND USAGE PATTERNS DEFINING A BUSINESS PROCESS Initial Example The Structure of a Business Process Language Extensibility The Lifecycle of a Business Process PARTNER LINK TYPES, PARTNER LINKS, AND ENDPOINT REFERENCES Partner Link Types Partner Links Business Partners Endpoint References MESSAGE PROPERTIES Motivation Defining Properties DATA HANDLING Expressions Boolean Expressions [8] Deleted: [9]... [10] Deleted: 11 Deleted: [11]... [12] Deleted: [13] Deleted: Feature... [14]... [15] Deleted: 12 Deleted: Other changes... [16] Deleted: [17]... [18] Deleted: [19] Deleted: [20] Deleted: [21] Deleted: [22] Deleted: [23] Deleted: 31 Deleted: SERVICE LINKING,... [24]... [25] Deleted: [26]... [27] Deleted: 7.1 Service Linking... [28] Deleted: [29] Deleted: 7.2 Partners... [30] Deleted: [31] Deleted: 7.3 Service... [32]... [33] Deleted: 35 Formatted... [34]... [35] Deleted: 8 Message Properties Deleted: 36 Formatted Formatted... [36]... [37]... [38]... [39]... [40] Formatted... [41]... [42]... [43]

5 Deleted: 3 Duration Deadline-Valued Expressions Duration-Valued Expressions General Expressions Variables Assignment Type Compatibility in Assignment Assignment Example CORRELATION Message Correlation Defining and Using Correlation Sets BASIC ACTIVITIES Standard Attributes for Each Activity Standard Elements for Each Activity Invoking Web Service Operations Providing Web Service Operations Updating Variable Contents Signaling Faults Waiting Doing Nothing STRUCTURED ACTIVITIES Sequence Switch While Pick Flow Link Semantics Dead-Path-Elimination (DPE) Flow Graph Example Links and Structured Activities SCOPES [47] Deleted: [48]... [49] Deleted: 4 General Deleted: [50] Formatted... [51]... [52] Deleted: 9.2 Variables... [53] Deleted: [54] Deleted: 9.3 Assignment... [55] Deleted: 41 Formatted... [56]... [57] Deleted:.1 Type Compatibility in... [58] Deleted: [59] Deleted: 2 Example... [60] Deleted: [61] Formatted... [62]... [63] Deleted: 10 Correlation... [64] Deleted: 44 Formatted... [65] Formatted... [66]... [67] Deleted:.1 MESSAGE... [68] Deleted: 45 Formatted... [69]... [70] Deleted: 2 Defining and Using... [71]... [72] Deleted: 46 Formatted... [73]... [74] Deleted: 11 Basic Activities 5 Deleted: 47 Formatted Formatted Deleted: 11.1 STANDARD... [75]... [76]... [77]... [78]... [79]... [80] Formatted... [81]... [82]... [83]... [84]... [85]... [86]

6 Deleted: Data Handling Error Handling in Business Processes Compensation Handlers Defining a Compensation Handler Invoking a Compensation Handler Fault Handlers Implicit Fault and Compensation Handlers Semantics of Activity Termination Handling Faults That Occur Inside Fault and Compensation Handlers Event Handlers Message Events Alarm events Enablement of Events Processing of Events Disablement of Events Fault Handling Considerations Concurrency Considerations Serializable Scopes EXTENSIONS FOR EXECUTABLE PROCESSES Expressions Variables Assignment Correlation Web Service Operations Terminating a Service Instance Compensation Event Handlers EXTENSIONS FOR BUSINESS PROTOCOLS Variables Assignment EXAMPLES [89] Deleted: [90]... [91] Deleted: 72 Deleted: [92]... [93] Deleted: [94] Deleted: [95] Deleted: 78 Deleted: [96]... [97] Deleted: [98] Deleted: [99] Deleted: [100] Deleted: [101] Deleted: [102] Deleted: [103] Deleted: 83 Deleted: [104]... [105] Deleted: [106] Deleted: [107] Deleted: [108] Deleted: [109] Deleted: [110] Deleted: [111] Deleted: [112] Deleted: [113] Deleted: 14.6 Compensation Deleted: [114]... [115]... [116] Formatted... [117]... [118]... [119]... [120]

7 16.1 Shipping Service Service Description Message Properties Process Loan Approval Service Description Process Multiple Start Activities Service Description Process SECURITY CONSIDERATIONS ACKNOWLEDGMENTS REFERENCES APPENDIX A STANDARD FAULTS APPENDIX B ATTRIBUTES AND DEFAULTS APPENDIX C COORDINATION PROTOCOL Coordination Protocol for BPEL4WS Scopes APPENDIX D - XSD SCHEMAS BPEL4WS Schema Partner Link Type Schema Message Properties Schema Formatted... [124] Deleted: [125] Deleted:.1 Description... [126]... [127]... [128] Deleted: Message... [129]... [130] Deleted: [131] Deleted: Process... [132] Deleted: 91 Deleted: 16.2 Loan Approval Deleted: 92 Formatted Deleted: Service Formatted Deleted: 95 Deleted: Process Deleted: 96 Formatted... [133]... [134]... [135]... [136]... [137]... [138]... [139]... [140]... [141]... [142]... [143] Deleted: 16.3 Multiple Start... [144] Deleted: [145] Formatted... [146]... [147] Deleted: Service... [148]... [149] Deleted: [150] Deleted: Process 7 Deleted: 102 Formatted Deleted: 17 Security Deleted: 105 Formatted Deleted: 18 Deleted: [151]... [152]... [153]... [154]... [155]... [156]... [157]... [158]... [159]... [160]... [161]... [162]... [163]... [164]... [165]

8 1 Introduction The goal of the Web Services effort is to achieve universal interoperability between applications by using Web standards. Web Services use a loosely coupled integration model to allow flexible integration of heterogeneous systems in a variety of domains including business-to-consumer, business-to-business and enterprise application integration. The following basic specifications originally defined the Web Services space: SOAP, Web Services Description Language (WSDL), and Universal Description, Discovery, and Integration (UDDI). SOAP defines an XML messaging protocol for basic service interoperability. WSDL introduces a common grammar for describing services. UDDI provides the infrastructure required to publish and discover services in a systematic way. Together, these specifications allow applications to find each other and interact following a loosely coupled, platformindependent model. Systems integration requires more than the ability to conduct simple interactions by using standard protocols. The full potential of Web Services as an integration platform will be achieved only when applications and business processes are able to integrate their complex interactions by using a standard process integration model. The interaction model that is directly supported by WSDL is essentially a stateless model of synchronous or uncorrelated asynchronous interactions. Models for business interactions typically assume sequences of peer-to-peer message exchanges, both synchronous and asynchronous, within stateful, long-running interactions involving two or more parties. To define such business interactions, a formal description of the message exchange protocols used by business processes in their interactions is needed. The definition of such business protocols involves precisely specifying the mutually visible message exchange behavior of each of the parties involved in the protocol, without revealing their internal implementation. There are two good reasons to separate the public aspects of business process behavior from internal or private aspects. One is that businesses obviously do not want to reveal all their internal decision making and data management to their business partners. The other is that, even where this is not the case, separating public from private process provides the freedom to change private aspects of the process implementation without affecting the public business protocol. Business protocols must clearly be described in a platform-independent manner and must capture all behavioral aspects that have cross-enterprise business significance. Each participant can then understand and plan for conformance to the business protocol without engaging in the process of human agreement that adds so much to the difficulty of establishing cross-enterprise automated business processes today. What are the concepts required to describe business protocols? And what is the relationship of these concepts to those required to describe executable processes? To answer these questions, consider the following: Business protocols invariably include data-dependent behavior. For example, a supply-chain protocol depends on data such as the number of line items in an order, the total value of an order, or a deliver-by deadline. Defining business intent in these cases requires the use of conditional and time-out constructs. The ability to specify exceptional conditions and their consequences, including recovery sequences, is at least as important for business protocols as the ability to define the behavior in the "all goes well" case. Long-running interactions include multiple, often nested units of work, each with its own data requirements. Business protocols frequently require cross-partner 8

9 coordination of the outcome (success or failure) of units of work at various levels of granularity. If we wish to provide precise predictable descriptions of service behavior for crossenterprise business protocols, we need a rich process description notation with many features reminiscent of an executable language. The key distinction between public message exchange protocols and executable internal processes is that internal processes handle data in rich private ways that need not be described in public protocols. In thinking about the data handling aspects of business protocols it is instructive to consider the analogy with network communication protocols. Network protocols define the shape and content of the protocol envelopes that flow on the wire, and the protocol behavior they describe is driven solely by the data in these envelopes. In other words, there is a clear physical separation between protocol-relevant data and "payload" data. The separation is far less clear cut in business protocols because the protocol-relevant data tends to be embedded in other application data. BPEL4WS uses a notion of message properties to identify protocol-relevant data embedded in messages. Properties can be viewed as "transparent" data relevant to public aspects as opposed to the "opaque" data that internal/private functions use. Transparent data affects the public business protocol in a direct way, whereas opaque data is significant primarily to back-end systems and affects the business protocol only by creating nondeterminism because the way it affects decisions is opaque. We take it as a principle that any data that is used to affect the behavior of a business protocol must be transparent and hence viewed as a property. The implicit effect of opaque data manifests itself through nondeterminism in the behavior of services involved in business protocols. Consider the example of a purchasing protocol. The seller has a service that receives a purchase order and responds with either acceptance or rejection based on a number of criteria, including availability of the goods and the credit of the buyer. Obviously, the decision processes are opaque, but the fact of the decision must be reflected as behavior alternatives in the external business protocol. In other words, the protocol requires something like a switch activity in the behavior of the seller's service but the selection of the branch taken is nondeterministic. Such nondeterminism can be modeled by allowing the assignment of a nondeterministic or opaque value to a message property, typically from an enumerated set of possibilities. The property can then be used in defining conditional behavior that captures behavioral alternatives without revealing actual decision processes. BPEL4WS explicitly allows the use of nondeterministic data values to make it possible to capture the essence of public behavior while hiding private aspects. The basic concepts of BPEL4WS can be applied in one of two ways. A BPEL4WS process can define a business protocol role, using the notion of abstract process. For example, in a supply-chain protocol, the buyer and the seller are two distinct roles, each with its own abstract process. Their relationship is typically modeled as a partner link. Abstract processes use all the concepts of BPEL4WS but approach data handling in a way that reflects the level of abstraction required to describe public aspects of the business protocol. Specifically, abstract processes handle only protocol-relevant data. BPEL4WS provides a way to identify protocol-relevant data as message properties. In addition, abstract processes use nondeterministic data values to hide private aspects of behavior. It is also possible to use BPEL4WS to define an executable business process. The logic and state of the process determine the nature and sequence of the Web Service interactions conducted at each business partner, and thus the interaction protocols. While a BPEL4WS process definition is not required to be complete from a private implementation point of view, the language effectively defines a portable execution format for business processes that rely exclusively on Web Service resources and XML data. Moreover, such processes Deleted: service 9

10 execute and interact with their partners in a consistent way regardless of the supporting platform or programming model used by the implementation of the hosting environment. Even where private implementation aspects use platform-dependent functionality, which is likely in many if not most realistic cases, the continuity of the basic conceptual model between abstract and executable processes in BPEL4WS makes it possible to export and import the public aspects embodied in business protocols as process or role templates while maintaining the intent and structure of the protocols. This is arguably the most attractive prospect for the use of BPEL4WS from the viewpoint of unlocking the potential of Web Services because it allows the development of tools and other technologies that greatly increase the level of automation and thereby lower the cost in establishing cross-enterprise automated business processes. In summary, we believe that the two usage patterns of business protocol description and executable business process description require a common core of process description concepts. In this specification we clearly separate the core concepts from the extensions required specifically for the two usage patterns. The BPEL4WS specification is focused on defining the common core, and adds only the essential extensions required for each usage pattern. BPEL4WS defines a model and a grammar for describing the behavior of a business process based on interactions between the process and its partners. The interaction with each partner occurs through Web Service interfaces, and the structure of the relationship at the interface level is encapsulated in what we call a partner link. The BPEL4WS process defines how multiple service interactions with these partners are coordinated to achieve a business goal, as well as the state and the logic necessary for this coordination. BPEL4WS also introduces systematic mechanisms for dealing with business exceptions and processing faults. Finally, BPEL4WS introduces a mechanism to define how individual or composite activities within a process are to be compensated in cases where exceptions occur or a partner requests reversal. BPEL4WS is layered on top of several XML specifications: WSDL 1.1, XML Schema 1.0, and XPath1.0. WSDL messages and XML Schema type definitions provide the data model used by BPEL4WS processes. XPath provides support for data manipulation. All external resources and partners are represented as WSDL services. BPEL4WS provides extensibility to accommodate future versions of these standards, specifically the XPath and related standards used in XML computation. 2 Notational Conventions The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [13]. Namespace URIs of the general form "some-uri" represent some application-dependent or context-dependent URI as defined in RFC 2396 [14]. This specification uses an informal syntax to describe the XML grammar of the XML fragments that follow: The syntax appears as an XML instance, but the values indicate the data types instead of values. Grammar in bold has not been introduced earlier in the document, or is of particular interest in an example. Deleted: service 10

11 <-- description --> is a placeholder for elements from some "other" namespace (like ##other in XSD). Characters are appended to elements, attributes, and <!-- descriptions --> as follows: "?" (0 or 1), "*" (0 or more), "+" (1 or more). The characters "[" and "]" are used to indicate that contained items are to be treated as a group with respect to the "?", "*", or "+" characters. Elements and attributes separated by " " and grouped by "(" and ")" are meant to be syntactic alternatives. The XML namespace prefixes (defined below) are used to indicate the namespace of the element being defined. Examples starting with <?xml contain enough information to conform to this specification; other examples are fragments and require additional information to be specified in order to conform. XSD schemas and WSDL definitions are provided as a formal definition of grammars [xmlschema1] [WSDL]. 3 Relationship with WSDL BPEL4WS depends on the following XML-based specifications: WSDL 1.1, XML Schema 1.0, XPath 1.0 and WS-Addressing. Among these, WSDL has the most influence on the BPEL4WS language. The BPEL4WS process model is layered on top of the service model defined by WSDL 1.1. At the core of the BPEL4WS process model is the notion of peer-to-peer interaction between services described in WSDL; both the process and its partners are modeled as WSDL services. A business process defines how to coordinate the interactions between a process instance and its partners. In this sense, a BPEL4WS process definition provides and/or uses one or more WSDL services, and provides the description of the behavior and interactions of a process instance relative to its partners and resources through Web Service interfaces. That is, BPEL4WS defines the message exchange protocols followed by the business process of a specific role in the interaction. The definition of a BPEL4WS business process also follows the WSDL model of separation between the abstract message contents used by the business process and deployment information (messages and porttype versus binding and address information). In particular, a BPEL4WS process represents all partners and interactions with these partners in terms of abstract WSDL interfaces (porttypes and operations); no references are made to the actual services used by a process instance. However, the abstract part of WSDL does not define the constraints imposed on the communication patterns supported by the concrete bindings. Therefore a BPEL4WS process may define behavior relative to a partner service that is not supported by all possible bindings, and it may happen that some bindings are invalid for a BPEL4WS process definition. A BPEL4WS process is a reusable definition that can be deployed in different ways and in different scenarios, while maintaining a uniform application-level behavior across all of them. Note that the description of the deployment of a BPEL4WS process is out of scope for this specification. Deleted: and Deleted:. 11

12 The dependency on WS-Addressing [16] is meant to avoid inventing a private BPEL4WS mechanism for web service endpoint references such references are obviously a very general requirement in the usage of web services. 4 What Changed from BPEL4WS 1.0 The BPEL4WS 1.1 specification is an enhancement of the BPEL4WS 1.0 specification [15]. The 1.1 version has five new authors who brought a fresh viewpoint and deep industry experience. Their contributions are reflected in a number of enhancements in this version. The 1.1 version incorporates numerous corrections and clarifications based on the feedback received on the 1.0 version. In addition, the 1.1 version differs from the 1.0 version in the following substantive ways Core Concepts Clarification We believe that the two usage patterns of business protocol description and executable business process description require a common core of process description concepts. In the 1.1 version of the specification we clearly separate the core concepts from the extensions required specifically for the two usage patterns. The main body of the specification defines the core concepts. The Extensions for Executable Processes and the Extensions for Business Protocols are defined in separate sections at the end of the specification. The separation of core concepts from extensions allows features required for specific usage patterns to be defined in a composable manner. It is conceivable that further extensions will be developed over time as the usage of the specification matures Terminology Changes The following terminology changes have occurred Service Links are now called Partner Links Service Link Types are now called Partner Link Types Service References are now called Endpoint References Containers are now called Variables The formal syntax has also been changed to reflect these terminology changes, including the replacement of the current partner element with a partnerlink element to reflect the fact that such a link is a conversational interface rather than reflective of a business relationship. A partner element reflective of a business relationship is added as described in the next section Feature Changes The following changes have been made The terminate activity is now strictly limited to executable processes. Partner Link Type Roles are now limited to a single WSDL porttype. A new partner element is added to allow grouping of Partner Links based on expected business enterprise relationships. Deleted: <#>Feature enhancements The 1.1 version adds <#>Variables and correlation sets that are associated with scopes rather than with the process as a whole. This permits easier management of visibility and lifetime for variables and repeated initiation of local correlation sets to allow multiple correlated conversations during, e.g., iterative behavior. <#>Event handlers which permit a process or scope to be prepared to receive external events and requests concurrently with the main activity of the process or scope. This is especially helpful for events and requests that cannot be scheduled relative to the main activity, but may occur at unpredictable times. <#>Other changes <#>The schema has been substantially updated to reflect both the feature enhancements and other needed corrections and simplification. <#>The term container for process data entities has been replaced with the more traditional variable. Formatted: Bullets and Numbering 12

13 Endpoint references (formerly service references) are now defined as given in WS- Addressing [16]. Message Properties are now limited to only be simple types. Web service interactions in abstract processes are now permitted to omit references to variables for inbound and outbound message data. Opaque assignment in abstract processes may now target Boolean variables, and variables of simple but unbounded types. In the latter case the semantics requires creation of a unique value similar to a GUID. The syntax for defining variables has been changed to use three mutually exclusive attributes messagetype, type and element. The first points to a WSDL message type definition. The second points to an XML Schema simple type. The third points to an XML Schema global element definition. This allows one to define variables using something other than WSDL message types. Only variables that are defined using messagetypes can be used as input or output targets in messaging operations. The ability to provide an in-line WSDL message type has been removed, since the vast majority of the uses of this feature will be replaced by the usage of XML Schema simple types and global elements. Correlation sets have now been added to the uniqueness requirement so that it is not legal to have two web service interactions outstanding if they have the same partner, port type, operation and correlation set(s). In case of activity termination, the activities wait, reply and invoke are added to receive as being instantly terminated rather than being allowed to finish. The variable provided as the value of the faultvariable attribute in a catch handler to hold fault data is now scoped to the fault handler itself rather than being inherited from the associated scope. Variables and correlation sets can now be associated with local scopes rather than with the process as a whole. This permits easier management of visibility and lifetime for variables and repeated initiation of local correlation sets to allow multiple correlated conversations during, e.g., iterative behavior. Event handlers can now be associated with scopes, to permit a process or scope to be prepared to receive external events and requests concurrently with the main activity of the process or scope. This is especially helpful for events and requests that cannot be scheduled relative to the main activity, but may occur at unpredictable times. The Future Directions section has been dropped since this version forms the starting point for a formal standards process, which will define those directions. 5 Core Concepts and Usage Patterns Formatted: Bulleted + Level: 1 + Aligned at: 0.25" + Tab after: 0.5" + Indent at: 0.5" As noted in the introduction, we believe that the two usage patterns of business protocol description and executable business process description require a common core of process description concepts. In this specification we clearly separate the core concepts from the extensions required specifically for the two usage patterns. The BPEL4WS specification is focused on defining the common core, and adds only the essential extensions required for each usage pattern. These extensions are described in separate sections (Extensions for Executable Processes and Extensions for Business Protocols). 13

14 In a number of cases, the behavior of a process in a certain combination of circumstances is undefined, e.g., when a variable is used before being initialized. In the definition of the core concepts we simply note that the semantics in such cases is not defined. BPEL4WS takes it as a general principle that compliant implementations MAY choose to perform static analysis to detect and reject process definitions that may have undefined semantics. Such analysis is necessarily pessimistic and therefore might in some cases prevent the use of processes that would not, in fact, create situations with undefined semantics, either in specific uses or in any use. In the executable usage pattern for BPEL4WS, situations of undefined semantics always result in standard faults in the BPEL4WS namespace. These cases will be described as part of the_extensions_for_executable_processes in the specification. However, it is important to note that BPEL4WS uses two standard internal faults for its core control semantics, namely, bpws:forcedtermination and bpws:joinfailure. These are the only two standard faults that play a role in the core concepts of BPEL4WS. Of course, the occurrence of faults specified in WSDL porttype definitions during web service invocation is accounted for in the core concepts as well. 6 Defining a Business Process 6.1 Initial Example Before describing the structure of business processes in detail, this section presents a simple example of a BPEL4WS process for handling a purchase order. The aim is to introduce the most basic structures and some of the fundamental concepts of the language. The operation of the process is very simple, and is represented in the following figure. Dotted lines represent sequencing. Free grouping of sequences represents concurrent sequences. Solid arrows represent control links used for synchronization across concurrent activities. Note that this is not meant to be a definitive graphical notation for BPEL4WS processes. It is used here informally as an aid to understanding. On receiving the purchase order from a customer, the process initiates three tasks concurrently: calculating the final price for the order, selecting a shipper, and scheduling the production and shipment for the order. While some of the processing can proceed concurrently, there are control and data dependencies between the three tasks. In particular, the shipping price is required to finalize the price calculation, and the shipping date is required for the complete fulfillment schedule. When the three tasks are completed, invoice processing can proceed and the invoice is sent to the customer. 14

15 Receive Purchase Order Initiate Price Calculation Decide On Shipper Initiate Production Scheduling Complete Price Calculation Arrange Logistics Complete Production Scheduling Invoice Processing The WSDL porttype offered by the service to its customers (purchaseorderpt) is shown in the following WSDL document. Other WSDL definitions required by the business process are included in the same WSDL document for simplicity; in particular, the porttypes for the Web Services providing price calculation, shipping selection and scheduling, and production scheduling functions are also defined there. Observe that there are no bindings or service elements in the WSDL document. A BPEL4WS process is defined "in the abstract" by referencing only the porttypes of the services involved in the process, and not their possible deployments. Defining business processes in this way allows the reuse of business process definitions over multiple deployments of compatible services. The partner link types included at the bottom of the WSDL document represent the interaction between the purchase order service and each of the parties with which it interacts (see Partner Link Types, Partner Links, and Endpoint References). Partner link types can be used to represent dependencies between services, regardless of whether a BPEL4WS business process is defined for one or more of those services. Each partner link type defines up to two "role" names, and lists the porttypes that each role must support for the interaction to be carried out successfully. In this example, two partner link types, "purchasinglt" and "schedulinglt", list a single role because, in the corresponding service interactions, one of the parties provides all the invoked operations: The "purchasinglt" partner link represents the connection between the process and the requesting customer, where only the purchase order service needs to offers a service operation ("sendpurchaseorder"); the "schedulinglt" partner link represents the interaction between the purchase order service and the scheduling service, in which only operations of the latter are invoked. The two other partner link types, "invoicinglt" and "shippinglt", define two roles because both the user of the invoice calculation and the user of the shipping service Deleted: service Deleted: Service Deleted: Service Linking, Partners, and Service References Deleted: service Deleted: purchaselt Deleted: purchaselt" service Deleted: service Deleted: service Deleted: invoicelt 15

16 (the invoice or the shipping schedule) must provide callback operations to enable asynchronous notifications to be asynchronously sent ("invoicecallbackpt" and "shippingcallbackpt" porttypes). <definitions targetnamespace=" xmlns:sns=" xmlns:pos=" xmlns:xsd=" xmlns=" xmlns:plnk=" Deleted: slnk Deleted: 03/service <import namespace=" location=" <message name="pomessage"> <part name="customerinfo" type="sns:customerinfo"/> <part name="purchaseorder" type="sns:purchaseorder"/> </message> <message name="invmessage"> <part name="ivc" type="sns:invoice"/> </message> <message name="orderfaulttype"> <part name="probleminfo" type="xsd:string"/> </message> <message name="shippingrequestmessage"> <part name="customerinfo" type="sns:customerinfo"/> </message> <message name="shippinginfomessage"> <part name="shippinginfo" type="sns:shippinginfo"/> </message> <message name="schedulemessage"> <part name="schedule" type="sns:scheduleinfo"/> </message> <!-- porttypes supported by the purchase order process --> <porttype name="purchaseorderpt"> <operation name="sendpurchaseorder"> 16

17 <input message="pos:pomessage"/> <output message="pos:invmessage"/> <fault name="cannotcompleteorder" message="pos:orderfaulttype"/> </operation> </porttype> <porttype name="invoicecallbackpt"> <operation name="sendinvoice"> <input message="pos:invmessage"/> </operation> </porttype> <porttype name="shippingcallbackpt"> <operation name="sendschedule"> <input message="pos:schedulemessage"/> </operation> </porttype> <!-- porttype supported by the invoice services --> <porttype name="computepricept"> <operation name="initiatepricecalculation"> <input message="pos:pomessage"/> </operation> <operation name="sendshippingprice"> <input message="pos:shippinginfomessage"/> </operation> </porttype> <!-- porttype supported by the shipping service --> <porttype name="shippingpt"> <operation name="requestshipping"> <input message="pos:shippingrequestmessage"/> <output message="pos:shippinginfomessage"/> <fault name="cannotcompleteorder" message="pos:orderfaulttype"/> </operation> </porttype> 17

18 <!-- porttype supported by the production scheduling process --> <porttype name="schedulingpt"> <operation name="requestproductionscheduling"> <input message="pos:pomessage"/> </operation> <operation name="sendshipingschedule"> <input message="pos:schedulemessage"/> </operation> </porttype> <plnk:partnerlinktype name="purchasinglt"> <plnk:role name="purchaseservice"> <plnk:porttype name="pos:purchaseorderpt"/> </plnk:role> </plnk:partnerlinktype> <plnk:partnerlinktype name="invoicinglt"> <plnk:role name="invoiceservice"> <plnk:porttype name="pos:computepricept"/> </plnk:role> <plnk:role name="invoicerequester"> <plnk:porttype name="pos:invoicecallbackpt"/> </plnk:role> </plnk:partnerlinktype> <plnk:partnerlinktype name="shippinglt"> <plnk:role name="shippingservice"> <plnk:porttype name="pos:shippingpt"/> </plnk:role> <plnk:role name="shippingrequester"> <plnk:porttype name="pos:shippingcallbackpt"/> </plnk:role> </plnk:partnerlinktype> <plnk:partnerlinktype name="schedulinglt"> <plnk:role name="schedulingservice"> Deleted: slnk:servicelinktype Deleted: purchaselt"> Deleted: slnk Deleted: slnk Deleted: slnk Deleted: slnk:servicelinktype > Deleted: <slnk:servicelinktype Deleted: invoicelt"> Deleted: slnk Deleted: slnk Deleted: slnk Deleted: slnk Deleted: slnk Deleted: slnk:servicelinktype > Deleted: <slnk:servicelinktype Deleted: slnk Deleted: slnk Deleted: slnk Deleted: slnk Deleted: slnk Deleted: slnk:servicelinktype > Deleted: <slnk:servicelinktype Deleted: slnk 18

19 <plnk:porttype name="pos:schedulingpt"/> </plnk:role> </plnk:partnerlinktype> Deleted: slnk Deleted: slnk Deleted: slnk:servicelinktype </definitions> The business process for the order service is defined next. There are four major sections in this process definition: The <variables> section defines the data variables used by the process, providing their definitions in terms of WSDL message types, XML Schema simple types, or XML Schema elements. Variables allow processes to maintain state data and process history based on messages exchanged. The <partnerlinks> section defines the different parties that interact with the business process in the course of processing the order. The four partnerlinks shown here correspond to the sender of the order (customer), as well as the providers of price (invoicingprovider), shipment (shippingprovider), and manufacturing scheduling services (schedulingprovider). Each partner link is characterized by a partner link type and a role name. This information identifies the functionality that must be provided by the business process and by the partner service for the relationship to succeed, that is, the porttypes that the purchase order process and the partner need to implement. The <faulthandlers> section contains fault handlers defining the activities that must be performed in response to faults resulting from the invocation of the assessment and approval services. In BPEL4WS, all faults, whether internal or resulting from a service invocation, are identified by a qualified name. In particular, each WSDL fault is identified in BPEL4WS by a qualified name formed by the target namespace of the WSDL document in which the relevant porttype and fault are defined, and the ncname of the fault. It is important to note, however, that because WSDL 1.1 does not require that fault names be unique within the namespace where the operation is defined, all faults sharing a common name and defined in the same namespace are indistinguishable. In spite of this serious WSDL limitation, BPEL4WS provides a uniform naming model for faults, in the expectation that future versions of WSDL will provide a better fault-naming model. The rest of the process definition contains the description of the normal behavior for handling a purchase request. The major elements of this description are explained in the section following the process definition. Deleted: partners Deleted: partners Deleted: invoiceprovider Deleted: service <process name="purchaseorderprocess" targetnamespace=" xmlns=" xmlns:lns=" <partnerlinks> <partnerlink name="purchasing" partnerlinktype="lns:purchasinglt" Deleted: <partners> <partner name="customer" servicelinktype="lns:purchas elt" 19

20 myrole="purchaseservice"/> <partnerlink name="invoicing" partnerlinktype="lns:invoicinglt" myrole="invoicerequester" partnerrole="invoiceservice"/> <partnerlink name="shipping" partnerlinktype="lns:shippinglt" myrole="shippingrequester" partnerrole="shippingservice"/> <partnerlink name="scheduling" partnerlinktype="lns:schedulinglt" partnerrole="schedulingservice"/> </partnerlinks> Deleted: <partner name="invoiceprovider" servicelinktype="lns:invoice LT" Deleted: partner Deleted: Provider Deleted: servicelinktype Deleted: partner Deleted: Provider Deleted: servicelinktype Deleted: partners <variables> <variable name="po" messagetype="lns:pomessage"/> <variable name="invoice" messagetype="lns:invmessage"/> <variable name="pofault" messagetype="lns:orderfaulttype"/> <variable name="shippingrequest" messagetype="lns:shippingrequestmessage"/> <variable name="shippinginfo" messagetype="lns:shippinginfomessage"/> <variable name="shippingschedule" messagetype="lns:schedulemessage"/> </variables> <faulthandlers> <catch faultname="lns:cannotcompleteorder" faultvariable="pofault"> <reply partnerlink="purchasing" porttype="lns:purchaseorderpt" operation="sendpurchaseorder" variable="pofault" faultname="cannotcompleteorder"/> </catch> </faulthandlers> Deleted: ="customer 20

21 <sequence> <receive partnerlink="purchasing" porttype="lns:purchaseorderpt" operation="sendpurchaseorder" variable="po"> </receive> Deleted: ="customer <flow> <links> <link name="ship-to-invoice"/> <link name="ship-to-scheduling"/> </links> <sequence> <assign> <copy> <from variable="po" part="customerinfo"/> <to variable="shippingrequest" part="customerinfo"/> </copy> </assign> <invoke partnerlink="shipping" porttype="lns:shippingpt" operation="requestshipping" inputvariable="shippingrequest" outputvariable="shippinginfo"> <source linkname="ship-to-invoice"/> </invoke> Deleted: ="shippingprovider <receive partnerlink="shipping" porttype="lns:shippingcallbackpt" operation="sendschedule" variable="shippingschedule"> <source linkname="ship-to-scheduling"/> Deleted: ="shippingprovider 21

22 </receive> </sequence> <sequence> <invoke partnerlink="invoicing" porttype="lns:computepricept" operation="initiatepricecalculation" inputvariable="po"> </invoke> <invoke partnerlink="invoicing" porttype="lns:computepricept" operation="sendshippingprice" inputvariable="shippinginfo"> <target linkname="ship-to-invoice"/> </invoke> Deleted: ="invoiceprovider Deleted: ="invoiceprovider <receive partnerlink="invoicing" porttype="lns:invoicecallbackpt" operation="sendinvoice" variable="invoice"/> Deleted: ="invoiceprovider </sequence> <sequence> <invoke partnerlink="scheduling" porttype="lns:schedulingpt" operation="requestproductionscheduling" inputvariable="po"> </invoke> <invoke partnerlink="scheduling" porttype="lns:schedulingpt" operation="sendshippingschedule" inputvariable="shippingschedule"> <target linkname="ship-to-scheduling"/> </invoke> </sequence> Deleted: ="schedulingprovider Deleted: ="schedulingprovider 22

23 </flow> <reply partnerlink="purchasing" porttype="lns:purchaseorderpt" operation="sendpurchaseorder" variable="invoice"/> </sequence> Deleted: ="customer </process> The structure of the main processing section is defined by the outer <sequence> element, which states that the three activities contained inside are performed in order. The customer request is received (<receive> element), then processed (inside a <flow> section that enables concurrent behavior), and a reply message with the final approval status of the request is sent back to the customer (<reply>). Note that the <receive> and <reply> elements are matched respectively to the <input> and <output> messages of the "sendpurchaseorder" operation invoked by the customer, while the activities performed by the process between these elements represent the actions taken in response to the customer request, from the time the request is received to the time the response is sent back (reply). The example makes the implicit assumption that the customer request can be processed in a reasonable amount of time, justifying the requirement that the invoker wait for a synchronous response (because this service is offered as a request-response operation). When that assumption does not hold, the interaction with the customer is better modeled as a pair of asynchronous message exchanges. In that case, the "sendpurchaseorder" operation is a one-way operation and the asynchronous response is sent by invoking a second one-way operation on a customer "callback" interface. In addition to changing the signature of "sendpurchaseorder" and defining a new porttype to represent the customer callback interface, two modifications need to be made in the preceding example to support an asynchronous response to the customer. First, the partner link type "purchasinglt" that represents the process-customer connection needs to include a second role ("customer") listing the customer callback porttype. Second, the <reply> activity in the process needs to be replaced by an <invoke> on the customer callback operation. The processing taking place inside the <flow> element consists of three <sequence> blocks running concurrently. The synchronization dependencies between activities in the three concurrent sequences are expressed by using "links" to connect them. The links are defined inside the flow and are used to connect a source activity to a target activity. (Note that each activity declares itself as the source or target of a link by using the nested <source> and <target> elements.) In the absence of links, the activities nested directly inside a flow proceed concurrently. In the example, however, the presence of two links introduces control dependencies between the activities performed inside each sequence. For example, while the price calculation can be started immediately after the request is received, shipping price can only be added to the invoice after the shipper information has been obtained; this dependency is represented by the link (named "ship-to-invoice") that connects the first call on the shipping provider ("requestshipping") with sending shipping information to the price calculation service ("sendshippingprice"). Likewise, shipping scheduling information can only be sent to the manufacturing scheduling service after it has been received from the shipper service; thus the need for the second link ("ship-to-scheduling"). Deleted: service Deleted: purchaselt 23